If you note the cake doesn't seem to be the one her Cake Sphere describes...there aren't nearly enough injector need guns and not enough rhubarbs or fish shaped solid waste.
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Ben BrockaJan 20 '13 at 22:45

You can actually get to the room with the cake, but it's tricky. My guess is that GLaDOS made that cake for herself and had no intention of sharing it.
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BrianMay 3 '13 at 16:46